The survey also bolsters the claim of Amazon CEO Jeff Bezos that iPad owners are buying Kindles: 40% of iPad users surveyed already own one, and 23% plan to buy one in the next year. According to J.P. Morgan analyst Imran Khan, the big price difference between the two devices--$139 for the low-end Kindle versus $499 for the cheapest iPad--really places them in different categories.

Khan also pointed out that overall e-book revenue is exploding, going from 1% of overall book revenue in 2008 to 9% in 2010. It could begin to cannibalize sales of physical books at retailers--one reason why Barnes and Noble is making such a big push with its own e-reader, the Nook. The survey showed that 45% of respondents had heard of the Nook, versus 76% for the Kindle and 84% for the iPad.

Overall, Khan rates Amazon as one of his top Internet stock picks for 2011, citing big opportunities for international penetration and better margins from growth in relatively new sectors like apparel, along with the rise in e-books.

Disclosure: Jeff Bezos is an investor in Business Insider through his
personal investment company Bezos Expeditions.